Dion-Kirschner: Lessons from scientists’ search for exoplanets

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On Feb. 22, NASA announced the discovery of seven Earth-sized exoplanets. Researchers believe all of the seven planets in the planetary system TRAPPIST-1 are rocky planets like Earth, rather than gaseous ones like Jupiter, Uranus and Neptune. Further, three of the identified planets orbit their parent star within the “habitable zone,” which describes the area around a star where planetary temperatures are most likely to allow for liquid water, a prerequisite for life.

For individual scientists in search of exoplanets, and really for the entire scientific community, this discovery is thrilling. The TRAPPIST-1 system, which contains the greatest number of potentially habitable planets discovered orbiting a single star, has been described by its researchers as a leading candidate for the study of atmospheres on Earth-like planets. Even to those uninterested by scientific developments, the thought of these distant planets and their potential to sustain life can be enthralling — maybe evoking images of Star Wars-like worlds where two moons light the sky and bizarre life forms abound.

But apart from bolstering our hope that Wookiees may exist somewhere, the search for Earth-like planets drives home an important point: The planet we live on has an exceedingly rare combination of characteristics that can support life. An entire scientific field’s worth of researchers, armed with ever-improving technology, are searching for other planets capable of sustaining life. The difficulty of their task highlights humanity’s incredible cosmic fortune.

In part, the discovery of TRAPPIST-1 is so exciting because the characteristics required for a planet to sustain life are highly specific. These planets are promising candidates, but to date no planet other than Earth has been confirmed to fit the bill. Most mainstream scientific consensus states that life requires a terrestrial (rocky) planet, an energy source, the correct chemical building blocks and liquid water. Of more than 3,000 confirmed exoplanets, fewer than 400 fulfill even the first requirement.

A subset of these planets exists in the habitable zone, where temperatures favor liquid water. The narrowness of this temperature range is reflected by the zone’s other name, the “Goldilocks zone”: if temperatures aren’t just right, water only exists as vapor or ice. So far, only Earth is known to have water in its liquid form, though it is believed that with improving technologies, one day we will find more liquid water outside our solar system.

And though some planets may hold all of the necessary resources, a very particular sequence of events must take place to form a living organism from nonliving building blocks. Chemistry must occur in just the right way, combining simple molecules into more complex prebiotic compounds, and finally into units that can grow and self-replicate — all by chance. Researchers still haven’t arrived at a consensus on how all of this could have happened here on Earth, let alone on planets outside our solar system. The fact that Earth meets the requirements for life, that each chemical step fell into place creating the first microorganisms and that life then evolved into the incredibly varied forms we have today, all adds up to a chain of lucky, but highly unlikely, events.

It is likely that one day, possibly in our own lifetimes, extraterrestrial life will be found. In such a vast universe, the chance that Earth is the only planet suitable for life is certainly slim. Nevertheless, from both the intense excitement sparked by the TRAPPIST-1 discovery and the consistent challenges in the search for Earth-like planets, it should be clear we are a lucky species indeed to exist at all. As NASA’s count of exoplanets continues to rise, let’s count our blessings and remember to be grateful for the planet that sustains us.

Hannah Dion-Kirschner is a junior in Weinberg and Bienen. She can be reached at hannahdionkirschner2018@u.northwestern.edu. If you would like to respond publicly to this column, send a Letter to the Editor to opinion@dailynorthwestern.com. The views expressed in this piece do not necessarily reflect the views of all staff members of The Daily Northwestern.